DirectionsActive time: 20 minutes
Total time: 1 hour, 15 minutes
Preheat oven to 425°. In a food processor, pulse sage, Parmigiano-Reggiano, pine nuts, 1 tsp. salt, and garlic a few times, just until roughly chopped. With the motor running, add 1/3 cup oil in a steady stream. Puree pesto until almost smooth, then set aside.
In a large bowl, mix onions with remaining 2 Tbsp. oil and 1 1/2 tsp. salt. Arrange onions in a single layer on a large rimmed baking sheet and bake, stirring occasionally, until deep golden brown and very tender, 45 minutes to 1 hour.
Transfer onions to a platter and spoon reserved pesto on top.
Adapted from 2012's A Girl and Her Pig, by April Bloomfield (Ecco).